In some cases, it is desirable to hydrogenate rubber to improve resistance to oxidative and thermal degradation. For example, it is sometimes beneficial to hydrogenate nitrile rubbers which are utilized in applications where there is exposure to high operating temperatures. The hydrogenation of polymers has conventionally been accomplished by solution techniques which require the use of highly reactive chemicals or heterogeneous catalysts. Unfortunately, such techniques present handling and application difficulties. However, these difficulties are overcome by hydrogenating the rubber in latex form as described in U.S. Pat. No. 4,452,950 to Lawson G. Wideman.
The process disclosed by Wideman involves the hydrogenation of carbon-carbon double bonds of an unsaturated polymer which comprises (a) combining an unsaturated polymer in latex form with (1) an oxidant selected from the group consisting of oxygen, air and hydroperoxides: (2) a reducing agent selected from the group of hydrazine and hydrates thereof: and (3) a metal ion initiator: and (b) heating the mixture to a temperature from 0.degree. C. to the reflux temperature of the reaction mixture. There are, of course, many advantages associated with hydrogenating the elastomeric polymer in latex form by the process of Wideman. However, there are difficulties which must be overcome to make the process described by Wideman commercially viable. For example, when high degrees of saturation are attained by the Wideman process, crosslinking of the polymer within the individual latex particles typically occurs. This is due to crosslinking of the elastomeric polymer which occurs during the reduction procedure. Such crosslinking is often undesirable with it usually being preferred for the elastomeric polymer to be uncrosslinked. Another problem encountered is the presence of residual hydrazine in the emulsion of the hydrogenated elastomeric polymer. The presence of high levels of residual hydrazine in the latex is commercially unacceptable. In fact, it is highly desirable for the level of residual hydrazine in the latex to be less than about 10 ppm (parts per million). In most cases, it is preferred for the concentration of residual hydrazine in the latex to be less than about 4 ppm.